The current unit selectors for quotas requires an increase of 10*1024 before accepting the next unit level. Most unit selectors, such as disk space indicators in Unix and Windows, use the next unit level at 1024 or above, not 10*1024. In other words, Webmin display 5 MB as 5120 KB. It does not change the units to MB until it reaches 10240 KB, but it should do this at 1024 KB. So, 1024 KB should be displayed as 1 MB, and 1536 KB should be displayed as 1.5 MB, etc.
Quota units selection