It is undoubtedly some sort of subtle formatting issue, to which the mac element or perhaps your version of SoundForge may contribute.
Certain formats are limited to 2 GB in size. FAT16 is limited to 2GB, thus the recorders nearly all of us use produce files that stop at 2 GB.
There are several different varieties of WAV formats. I thought some of those may also have a 2 GB limit, but it could be the program dependent rather than due to variants in WAV. Per our friend wikipedia "The WAV format is limited to files that are less than 4 GB, because of its use of a 32-bit unsigned integer to record the file size header some programs limit the file size to 2 GB. Although this is equivalent to about 6.8 hours of CD-quality audio (44.1 kHz, 16-bit stereo), it is sometimes necessary to exceed this limit, especially when greater sampling rates, bit resolutions or channel count are required. The W64 format was therefore created for use in Sound Forge. Its 64-bit header allows for much longer recording times."
It doesn't sound like it's an issue of your target drive's formatting since it seems you can save larger than 2 GB files in other formats? You could not for example save a file larger than 2 GB to a FAT formatted flash card since that format poses a 2 GB limit. NTFS (the more common Windows disk format) is limited to 4GB.