Why do my raster layers' data change when converting from SpatRaster to rasterStack?

Question

I have imported a multi-layer tiff file (7 "bio" layers) using the rast() function from terra and then added other layers to this from elsewhere using:

current.raster <- rast("./bio_layers.tif")

# add1, add2, and add3 are SpatRaster objects from tif files that were modified 
# in earlier steps and are stored in memory
new.rast <- c(current.raster, add1, add2, add3) 

new.rast
class       : SpatRaster 
dimensions  : 848, 3084, 10  (nrow, ncol, nlyr)
resolution  : 0.008333333, 0.008333333  (x, y)
extent      : -141, -115.3, 67.49167, 74.55833  (xmin, xmax, ymin, ymax)
coord. ref. : lon/lat WGS 84 (EPSG:4326) 
sources     : bio_layers.tif  (7 layers) 
              memory  
              memory  
              ... and 1 more source(s)

When I convert this to a rasterStack object using stack(), the values of the "add" layers are changed to become the values of the first layer of current.raster. See summary of my rasters below.

summary(new.rast)
      bio1             bio2            bio3             bio4           bio11            bio15           bio18       
 Min.   :-16.60   Min.   :1.00    Min.   : 12.29   Min.   : 0.00   Min.   :-32.15   Min.   :34.31   Min.   :  9.00  
 1st Qu.:-14.45   1st Qu.:6.95    1st Qu.: 15.29   1st Qu.:14.41   1st Qu.:-30.52   1st Qu.:55.30   1st Qu.: 53.00  
 Median :-11.74   Median :7.42    Median : 15.90   Median :14.67   Median :-27.87   Median :59.26   Median : 63.00  
 Mean   :-12.07   Mean   :7.53    Mean   : 16.19   Mean   :14.75   Mean   :-28.23   Mean   :59.21   Mean   : 70.24  
 3rd Qu.: -9.79   3rd Qu.:8.02    3rd Qu.: 16.79   3rd Qu.:15.27   3rd Qu.:-26.35   3rd Qu.:63.18   3rd Qu.: 83.00  
 Max.   :  0.00   Max.   :9.56    Max.   :100.00   Max.   :16.37   Max.   :  0.00   Max.   :91.12   Max.   :153.00  
 NA's   :78844    NA's   :78844   NA's   :78844    NA's   :78844   NA's   :78844    NA's   :78844   NA's   :78844   
      add1              add2            add3       
 Min.   : -15.42   Min.   : 0.00   Min.   :0.00   
 1st Qu.:  38.41   1st Qu.: 0.71   1st Qu.:0.00   
 Median : 114.79   Median : 1.74   Median :0.00   
 Mean   : 166.82   Mean   : 3.45   Mean   :0.00   
 3rd Qu.: 222.14   3rd Qu.: 3.84   3rd Qu.:0.00   
 Max.   :1584.36   Max.   :49.38   Max.   :0.02   
 NA's   :79057     NA's   :79326   NA's   :81712  

summary(stack(new.rast))
                 bio1         bio2         bio3         bio4         bio11        bio15   bio18          add1
Min.        -16.60000 1.000000e+00 1.253205e+01 0.000000e+00     -32.15000 3.511098e+01      10     -16.60000
1st Qu.     -14.45833 6.950000e+00 1.528698e+01 1.441101e+01     -30.51667 5.537055e+01      53     -14.45833
Median      -11.77917 7.425000e+00 1.589191e+01 1.467350e+01     -27.88333 5.927956e+01      63     -11.77917
3rd Qu.      -9.78750 8.016666e+00 1.679012e+01 1.526218e+01     -26.35000 6.308383e+01      83      -9.78750
Max.          0.00000 9.575000e+00 1.000000e+02 1.638678e+01       0.00000 8.897108e+01     148       0.00000
NA's    2046158.00000 2.046158e+06 2.046158e+06 2.046158e+06 2046158.00000 2.046158e+06 2046158 2046158.00000
                 add2          add3
Min.        -16.60000     -16.60000
1st Qu.     -14.45833     -14.45833
Median      -11.77917     -11.77917
3rd Qu.      -9.78750      -9.78750
Max.          0.00000       0.00000
NA's    2046158.00000 2046158.00000

Notice how the "add" layers data have changed to replicate the "bio1" layer. Why is this happening? Is there a way to preserve the data of these layers stored in memory as I convert it to a rasterStack object?