works as expected for me.

tested with and without spaces: works

Setting RTC - thanks for testing

I tested it local (Win7; xampp v3.2.1.; PHP Version 5.6.3), and get an error, when i took the spaces in the field-> Legal Extensions (File Types). The other fields works with spaces. The field-> Legal Extensions (File Types needs before and after a ","

Unsetting RTC

@Mumion - can you post the values that you have in Legal Extensions. I had another look at this and I can't reproduce your issue.

checked "Legal Extensions (File Types)" again ...
" bmp , csv,doc,gif,ico, jpg , jpeg ,odg, "
works fine on php 5.5.9-1ubuntu4.6

works fine for me.
cannot reproduce problem of @mumion
Tested fields:
Legal Extensions (File Types)
Legal Image Extensions (File Types)
Ignored Extensions
Legal MIME Types

Illegal MIME Types

with different kind of blanks before and after comma

I came across the following setup issue:
in com_media global options the field "Legal Image Extensions (File Types)" has the values: bmp,gif,jpg,png
In my opinion the value "jpeg" is missing.

In Template global options you are allowed to upload gif,bmp,jpg,jpeg,png

I don't know if there are any other places of this setup.

Field: "Legal Extensions (File Types)

bmp,csv,doc,gif,ico jpg jpeg odg,odp,ods,odt,pdf png ppt,swf,txt,xcf,xls,BMP,CSV,DOC,GIF,ICO,JPG,JPEG,ODG,ODP,ODS,ODT,PDF,PNG,PPT,SWF,TXT,XCF,XLS
-> with this pamrameters i get the notice: Dieser Dateityp wird nicht unterstützt. (This file type is not supported.)

When i change in this:
bmp,csv,doc,gif,ico,jpg,jpeg,odg,odp,ods,odt,pdf,png,ppt,swf,txt,xcf,xls,BMP,CSV,DOC,GIF,ICO,JPG,JPEG,ODG,ODP,ODS,ODT,PDF,PNG,PPT,SWF,TXT,XCF,XLS
-> its works fine.

The other fields works with spaces. I use the german translation pack, but i test also with the english translation.

I tested with a .jpg and .png file.

The fields:
Legal Image Extensions (File Types)
[Ignored Extensions (not tested)]
Legal MIME Types
Illegal MIME Types

works with spaces and without a patch.

Well, the fix doesn't handle he case when you don't enter any commas. It only fixes the issue when you have commas and spaces.
Entering file names without a comma is something that can't work. As the description of the field says (comma separated).

Ok, i misunderstood this.

Now, the patch works fine.

I tested with:

XAMPP v3.2.1, Joomla!-Version 3.4.1-dev, with blank before jpg as shown in the pic attached.

Result with patch:

Result without patch:

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Based on retests I am marking this RTc again