When a folder is selected, the size of the folder is displayed on the status bar. However, the folder size displayed on the status bar is incorrect: instead of showing the size of all the contents of the folder it only shows the size of the metadata (usually 4kb). Right-clicking the folder and selecting Proprieties shows the correct folder size.
When selecting files and folders together, Thunar will display the sum of file's sizes and 4 kb for each folder; this lead to an error, particularly when there are so many (large) files in folders.
The status bar display a wrong size for folder in thunar 1.4.0 And in the folder it display the right size only if don't have folder in it
Fixed in e20942b. Just hide the size of folders, no deep counting for performance reasons. The commits also changes the selection text to "X folders, X other items (XKb)".