An jpeg file with the following exif tags:

DateTime = DateTimeOriginal = DateTimeDigitized = 2001:12:21 15:13:07

After importing it to f-spot:

DateTime          = 2008:12:26 00:43:41
DateTimeOriginal  = 2001:12:21 12:13:07
DataTimeDigitized = 2001:12:21 15:13:07

I did not edit the image yet!

Why did f-spot updated the file? I see f-spot wrote "Software" exif tag with "f-spot version 0.5.0.3" value. I do not object, but... if I install newer version of f-spot, will it retag all my images (~12000) with new version string? 

But change in date is more important. I do not care too much about DateTime exif tag. Exif spec v2.2 says it is file change date and time, so, if f-spot wrote something to the file, changing DateTime may be correct. But why did f-spot changed DateTimeOriginal tag?? Here is a cite from Exif spec 2.2:

"The date and time when the image was stored as digital data. If, for example, an image was captured by DSC and at the same time the file was recorded, then the DateTimeOriginal and DateTimeDigitized will have the same contents."

Most of the cameras record images immediately after capturing, so DateTimeOriginal = DateTimeDigitized is a usual case. At least it is true for all my photos. I do not see any reason for changing DateTimeOriginal. 

I guess f-spot treated DateTimeDigitized as local time and left it untouched, and set DateTimeOriginal to the same time but in UTC (my local time is UTC+3). Exif spec says nothing about UTC and local time. Is there any widely adopted tradition to save UTC in DateTimeOriginal? Even if there is such a tradition, f-spot was not right, because there is no relation between my current local time and local time of imported roll. For example, my current local time is UTC+3, but pictures I imported to f-spot were taken in different place with different time, namely, UTC+5.

Thus: Please consider not changing DateTimeOriginal.