This problem occurs in the arabic mediawiki. When creating a page which has at the end of its text two or more category tags, and with no full-stop at the end of the text. The viewed text removes the space between the final two words, which make them appear as a single word.
Tracing the problem shows that it occurs at this line at Parser.php:
$s = rtrim( $s . "\n" ); # bug 87
It appears that when the rtrim removes the whitespace produced by the tags, the error occurs.
You can reproduce the bug by creating a page in the arabic wiki with the previous conditions. I have tried the following in the arabic sand box page.
"
testing space bug
testing space bug
[[تصنيف:الآداب]]
[[تصنيف:شعر عربي]]
"
outputs as:
"
testing space bug
testing spacebug
"
And
"
معاركنا انتهت أفلا تراني
رميت مهنّدي وكسرت رمحي
[[تصنيف:الآداب]]
[[تصنيف:شعر عربي]]
"
outputs as:
"
معاركنا انتهت أفلا تراني
رميت مهنّدي وكسرترمحي
"