How can I change the font for symbols in a formula?

Compare the plus sign with the dots around it (the one I don’t want) to the one before “27a2d” (the actual plus sign of the font I’m using, which I do want; that part isn’t a formula object but normal text). The minus signs and plus or minus are also affected, but at least I can paste those in manually. Even so, it’s an inconvenience.

Example plus sign problem

Refer the part of my answer here that deals with the minus sign and the related bug fdo#49547. Comment #7 provides a workaround by replacing the current OpenSymbol font with an older one (which was included with LO v3.3). Alternatively, you can obtain the thinner plus sign you require by using:

x {"+"} y

…rather than:

x + y