Gmail multi-attachments selection fails with certain themes

Is it just me or with some Gmail themes (Desk, Summer Ocean), you can't select multiple files to add as attachments (by clicking ctrl or shift in Windows)?

For other themes I tried, such as Ninja, Default, Classic, I was able to select multiple files at the same time as attachments. They offer a different pop-up window for you to select your file altogether.

The following shows up when I want to add attachments and I CAN'T select several files at the same time (notice the Desk theme):


Now notice the window I get when I try to add attachments with other themes, with which I CAN use ctrl to select several files at the same time:



As you can see the windows are different, which means maybe developers have different codes for certain themes so the bulk-attachments feature isn't available in Gmail always 100%. I naturally tried to Google to see if other users have experienced the same thing, but couldn't find anything. Perhaps, Desk users are on the low?

EDIT: Found some discussion forums that pointed out that indeed certain themes (Tree) didn't allow the multiple selection of attachments and that "There are three workarounds:
1. Click compose mail; then refresh the page
2. Click compose mail; pop-out the window (Icon above the upper right
corner of the "To" box)
3. Hold down shift, then click on compose mail (also pops out the
compose mail window)" Also found that the advanced selection features might not be available on some computers regardless of themes. I'll just switch to one that allows the features for now.